Johnson, Ned K. <br/><br/>
Character variation and evolution sibling species in the Empidonax difficilis-flavescens complex (Aves : tyrannidae) 

 - x, 151 pages:  illustration ;  26cm 
 - University of California publications in zoology ; vol 112 .
<br/><br/> Acc. No. 07967 
<br/><br/><label>ISBN: </label>0520095995 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Birds